It is sometimes desirable to adjust the rate at which fluid enters the tubes of a heat exchanger, either to have some tubes with a higher flow rate than others, or else to make the flow rate as uniform as possible over the various the tubes, taking account of flow conditions which tend to cause more fluid to flow from the feed chamber into some tubes than in to others.
Proposals have already been made to provide such fluid rate control by placing a relatively thin sheet against the perforated tube plate with said sheet having holes which are smaller in diameter than the holes through the perforated tube plate and which are disposed at the same locations. The fluid feeding the tubes of the bundle is thus constrained to pass through the smaller holes of the sheet prior to entering the tubes. In order to prevent fluid from flowing in the space between the tube plate and the sheet, which could give rise to unequal flow rates, the sheet must be clamped firmly against the face of the tube plate. Further, the clamping member(s) must be suitable for easy disassembly in order to provide access to the welds between the tubes in the bundle and the tube plate, whenever inspection or repair is necessary.
Given the diameter and the closeness of the holes through the tube plate, there is not enough room to install pins or screws in the tube plate for fixing the perforated sheet therto. Further, if the fixing means are installed in such a way as to block some of the holes through the tube plate, then the number of active tubes in the heat exchanger bundle is reduced.
The present invention seeks to provide a fixing device for fixing a perforated sheet against the perforated tube plate in order to control the rate of fluid flow along said tubes, said fixing device avoiding blocking any of the holes through the tube plate while nevertheless being easily disassembled in order to provide access to said holes.